Be sure to have Node.js 5.x+ installed.
Run npm install in the project root. This will install some build tools we use.
Run npm run watch to start a watcher that will compile things in place. You can then view the site by simply opening index.html.
Run npm run build to do a local build into the out/ directory. You can then preview the site at out/index.html. This should usually be the same as just index.html, but it is good to check before committing, since the build process is slightly more complicated than the in-place watch process.
Stylus is used for styling.
Handlebars is used for templating. index.hbs is minimally templated, mostly delegating to the partials in templates/. Those pull their data from data/. The logic that ties them all together is in build/templater.js.
Gulp is used for a build/watch system. This is abstracted behind npm tasks though (npm run watch, npm run build).
Traceur is used to write ES2015 code instead of boring-old-JavaScript, for the build code at least.
Travis is used to build and deploy the website to gh-pages on each push, per this guide.
The site is intended to be responsive, which we accomplish with per-device stylesheets and media queries in the HTML.
While editing you should be using an EditorConfig plugin for your text editor to enforce a few basic stylistic things.
We are trying to maintain a reasonable HTML document outline (so, don't use <section> as if it were <div>). To preview the document outline, use the HTML 5 Outliner tool; here's a direct link to the outline for the current version.